Report max interframe delay over window insdead of interframe delay sum

Maximum of interframe delay is calculated over moving window in
ReceiveStatistics proxy now and reported via GetStats. Name of a metric
is also changed.

BUG=none

Review-Url: https://codereview.webrtc.org/2995143002
Cr-Original-Commit-Position: refs/heads/master@{#19463}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: a79cc28de1fd7f0fa8e331e9bf3d8bbe2a24fa23
12 files changed